picked up 87 mustang 5.0 5 speed the body isnt the greatest but it runs good, sorta. it idles fine and drives good but when i floor it the car will take off but once it hits about 3500 rpm it falls right on its face. Let off the gas a bit and it picks right back up. Only messed with it for a few minutes so as far as i know i could be anything. The exhaust stinks bad like old gas so im hoping to get it out and put fresh in it will take care of it. any other suggestions?

Nice. I love those old fox body 'stangs. I have and '86 5.0HO in my jeep cj and have an '89 freshly dipped, waiting for me to decide what heads, etc I'm gonna put on it. You might want to use the mustang forums after you try fresh gas and the other obvious fixes. They've been really helpful to me when chasing gremlins. If you need anything, shoot me a pm and I'll point you towards the forum I used. Post pics up!

Fuel pump is my bet. Make sure you clean out the fuel tank if you end up putting a new one in. Find someone to let you use a fuel pressure gauge, you can easily tap into the schradder valve on the fuel rail. If you cant find one you can borrow that you can see while driving you may have to have a buddy ride under the hood while you floor it and watch the gauge lol. I had to do this once, long story, and yeah, bad idea lol.

yea just ut in the fresh gas, gotta go run it. got a pressure gauge gonna check that to. what should it have for pressure?

Off the top of my head I'd say 35-40 psi. Test in line off the test port. Test port is located on the fuel rail over top of the injectors. Sticking a screwdriver in the shrader valve of the test port and watching fuel spray out is not a confirmation of acceptable fuel pressure.

Fords use their own size test port on the fuel rail. If you have a standard pressure tester, you will be out of luck.

Make sure you watch teh fuel pressure at higher RPM under load where you had a problem. When my 5.0 thunderbird had a high RPM miss it showed good fuel pressure till it was under load and RPM came up and the fuel pressure just sank after a certain point.